Examination of a fundus of the eye is widely accepted as important in the early diagnosis of lifestyle-related diseases and diseases likely to cause blindness. Fundus cameras and scanning laser ophthalmoscopes (SLO) are among the apparatuses used for the inspection of the fundus of the eye. The fundus camera captures an image of a fundus of the eye by receiving reflected light of a light beam which has entered the fundus of the eye. The SLO is an ophthalmologic apparatus that uses the principle of confocal laser scanning microscope. In recent years, fundus cameras and SLOs including an adaptive optical system have been developed and are used for acquiring fundus planar images of high lateral resolution. The adaptive optical system measures an aberration of a subject's eye by a wavefront sensor in real time and corrects the aberration of the measuring beam and the return beam that occurs at the subject's eye by a wavefront correcting device. Further, attempts are being made to capture images of photoreceptor cells of a retina using by these apparatuses and make a diagnosis of a disease or evaluate drug response.
As an example of visualization of the photoreceptor cells using an adaptive optics SLO, Kaccie Y. Li and Austin Roorda, “Automated identification of cone photoreceptors in adaptive optics retinal images” J. Opt. Soc. Am. A, May 2007, Vol. 24, No. 5, 1358 discusses an ophthalmologic imaging apparatus which is capable of automated extraction of photoreceptor cells by acquiring a planar image of the fundus of the eye regarding the retina. According to this technique, a fundus planar image of a retina with high lateral resolution is acquired by preprocessing the acquired planar image, in other words, removing high frequency components from the planar image using periodicity of the arrangement of the photoreceptor cells visualized in the image.